BE SURE TO BACKUP ALL EEPROM AND HD LOCK CODES TO YOUR STOCK HD FIRST!!!!
use xboxhdm on your pc to build a stock hd image on your pc then ftp all the contents of your c and e drive (minus games and music and videos etc JUST THE SYSTEM FILES AND APPS/DASHBOARDS) to your pc and then add them to the image.
use the xboxhdm to create a boot disc on a cdr that contains the image file you made and the installer.
then turn off your pc and remove its HD and replace it with the new HD with jumper set as master.
turn on ur pc and insert the cdr into ur rom drive. it will boot from cd and give you all the options to create a new hard drive etc. check that the drive is unlocked before u begin. use the command to copy over BOTH the c and e drives of the image on cd.
this should format, partition and install all of the files that were on your stock HD including the softmod. RELOCK THE HARD DRIVE BEFORE YOU PROCEED.
remove the hd and reset the jumper to cable select and put it in your xbox.
should reboot normally.
any corrections etc please add
hope this helps